3+ • Hohmannite Fe2 O(SO4)2 8H2O c 2001-2005 Mineral Data Publishing, version 1 Crystal Data: Triclinic. Point Group: 1. Crystals are short prismatic along [001], to 1 mm, typically with dull or rounded and striated faces; as granular aggregates. Physical Properties: Cleavage: {010}, perfect; {110} and {110}, less perfect (referred to morphological axes; relation to X-ray axes uncertain). Hardness = 3 D(meas.) = 2.255 D(calc.) = 2.250 Decomposes in hot H2O; rapidly dehydrates to metahohmannite on exposure to air. Optical Properties: Transparent to translucent. Color: Chestnut-brown to burnt orange, pale amaranth-red. Streak: Yellow-orange. Luster: Vitreous, brilliant. Optical Class: Biaxial (–). Pleochroism: X = pale yellow; Y = pale greenish yellow; Z = dark greenish yellow. Orientation: Y ∧ c =23◦. Dispersion: r> v,extreme. α = 1.553–1.559 β = 1.643 γ = 1.655–1.657 2V(meas.) = 40◦ Cell Data: Space Group: P 1. a = 9.148(1) b = 10.922(1) c = 7.183(3) α =90.29(6)◦ β =90.79(4)◦ γ = 107.36(2)◦ Z=2 X-ray Powder Pattern: Sierra Gorda district, Chile. 7.92 (FFF), 8.69 (FF), 10.36 (F), 3.46 (F), 5.31 (mF), 3.12 (mF), 3.95 (mf) Chemistry: (1) (2) SO3 33.80 34.52 Fe2O3 33.92 34.42 H2O 30.76 31.06 insol. 1.15 Total 99.63 100.00 • (1) Sierra Gorda district, Chile. (2) Fe2O(SO4)2 8H2O. Occurrence: An uncommon low-temperature precipitate in oxidized iron sulfide deposits. Association: Metahohmannite, copiapite, amarantite, sideronatrite (Sierra Gorda district, Chile); chalcanthite, picromerite, amarantite, fibroferrite, copiapite (Chuquicamata, Chile); metahohmannite, sulfur, cinnabar (Redington mine, California, USA). Distribution: In Chile, in Antofagasta, from near Caracoles, Sierra Gorda district, and at Alcaparrosa, near Cerritos Bayos, both southwest of Calama; at Quetena, west of Calama; and from Chuquicamata. At the Redington mine, Knoxville, Napa Co., California, USA. From Saghand, Yazd, Iran. In the Plaka mine, near Laurium, Greece. Name: Honors Thomas Hohmann (1843–1897), mining engineer of Valparaiso, Chile who discovered the first specimens. Type Material: Mining Academy, Freiberg, Germany, 18623. References: (1) Palache, C., H. Berman, and C. Frondel (1951) Dana’s system of mineralogy, (7th edition), v. II, 613–614. (2) Scordari, F. (1978) The crystal structure of hohmannite, • • Fe2(H2O)4[(SO4)2O] 4H2O and its relationship to amarantite, Fe2(H2O)4[(SO4)2O] 3H2O. Mineral. Mag., 42, 144–146 and M9–M11. (3) Cesbron, F. (1964) Contribution `ala min´eralogie des sulfates de fer hydrat´es.Bull. Min´eral.,87, 125–143, esp. 134–135 (in French). All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise without the prior written permission of Mineral Data Publishing..